A computer operator typically inputs data through a keyboard and views the output via a video display screen. The location at which the information is entered relative to the screen is determined by the position of a cursor or cross-hair marker. The operator must be provided with a means of moving the cursor or other marker about the screen to enable data input at desired locations. As cursor positioning may be required at any location on the screen, means must be provided for both vertical and horizontal movement of the cursor. Accordingly, essentially every keyboard is provided with four cursor movement control keys which move the cursor straight up, straight down, straight left or straight right. Diagonal or other angled movements are generated by successive pushing of two of the cursor movement control keys.
With the advent of computer graphics and graphical user interfaces, pointing devices have been designed which enable the user to move a cursor quickly, easily and directly to any desired location on a screen. These devices include data tablets, mice, trackballs and joy sticks. Such devices are typically incorporated in a housing separate from the computer keyboard. Such consumes desk space, and is typically unsuited for portable computers such as the increasingly popular lap-top and notebook size computers. Trackballs have been incorporated into keyboards, but they typically consume a large amount of space.
It would be desirable to incorporate cursor/cross-hair movement control of any direction into a single key positioned within the confines of a conventional computer keyboard housing. Preferably, the size of such a key would be no greater than the existing size of any alphanumeric key on a keyboard. One such key is shown by way of example in U.S. Pat. No. 4,680,577. Sliding movements of such control key impart cursor movement on the screen.
Another more recent type of cursor movement control key employs force-sensitive resistors for registering operator key inputs. A force-sensitive resistor is typically comprised of two polymer sheets laminated or otherwise spaced closely relative to one another. One sheet is coated with spaced conductive interdigiting electrodes. The other sheet is coated with a polymer film which exhibits decreasing resistance with increasing force applied normal to the film surface. When force is applied to the opposing sheets, the conductive polymer material shunts the interdigiting electrodes to a greater or lesser degree depending upon the applied force. Thus, greater force results in greater current flow between the interdigiting electrodes.
Force-sensitive resistors were first developed for use in musical instruments such as electric drums and pianos, and as well have found use in electronic computer keyboard switches. Example construction and operation of force-sensitive resistors are explained in U.S. Pat. Nos. 4,268,815; 4,276,538; 4,301,337; 4,314,227; 4,314,228; 4,315,238; 4,451,714; 4,489,302; 4,739,299; 4,810,992; and 4,963,702, which are hereby incorporated by reference. Such force-sensitive resistors exhibiting a desired force-resistance relationship can be purchased through Interlink Electronics of Santa Barbara, Calif. and Carpenteria, Calif.
One prior art cursor movement control key for a computer having a video display, and which employs a force-sensitive resistor, is illustrated in FIG. 1A in partial section and designated with reference numeral 10. FIG. 1A is a partial diagrammatic section of a keyboard which supports an external key cap or body 12 for depression and tilting movement. Electronic computer keyboards include what is commonly referred to as a top mounting plate 14 and a bottom or backing plate 16. An actuator/housing 18 is suspended as shown within an opening 19 of mounting plate 14, and supports external key 12 for depression relative thereto. A rubber dome sheet 20 and switching membrane 22 are provided between actuator 18 and backing plate 16. Components or sheets 14, 20, 22, and 16 are typically each of a unitary construction extending throughout the keyboard key area.
Rubber dome sheet 20 functions as a biasing means for biasing the keys to their normal, extended positions using resiliently collapsible domes 15. Switching membrane 22 incorporates opposed conductive elements which function as on-off switches depending upon the relative position of external key 12. Switching membrane 22 also incorporates the above-described force-sensitive resistor material, as will be more fully described below. External cap 12 would be retained relative to actuator 18 by means of conventional spring clips (not shown) which also enable depression of cap 12 relative to actuator 18. Actuator 18 is retained relative to the keyboard by means of screws 24, screw plate 26, and adjustable spring 29, as will be more fully described below. FIG. 1A illustrates key 10 in its fully extended position, while FIG. 2A illustrates key 10 in a depressed condition. FIGS. 1B and 2B are enlarged sectional views of switching membrane 22 in its extended and depressed conditions, respectively.
More particularly and with reference to FIGS. 1A, 1B, 2A, 2B, 3 and 4, actuator 18 is of a rotated square-diamond shape, which is complementary to the size and shape of opening 19 in mounting plate 14. Actuator 18 includes three threaded holes 26 at its periphery which receive mounting and tension screws 24, for reasons which will be more fully described below. A raised portion 28 is provided in the center of actuator 18, and includes an opening or hole 30 extending therethrough. External key 12 includes a transverse stem 13 (FIGS. 1A, 2A) which is slidably received within opening 30. Key 12 and actuator 18 are constructed such that limited movement of key 12 is possible relative to actuator 18. Specifically, the length of stem 13 is sufficient such that depression of key 12 will cause collapsing of dome 15 of rubber dome sheet 20 and, at such point, cause engagement of a portion 17 of external key 12 with actuator raised portion 28. At this point, continued depression of key 12 transfers force and correspondingly limited movement directly to actuator 18 by such engagement.
Actuator 18 includes four actuator nodules 32 positioned diagonally relative to raised portion 28 from the underside of actuator 18 (FIG. 4). Actuator nodules 32 are so positioned for engagement with isolated conductive electrode regions of a force-sensitive resistor, which will become more apparent from the continuing discussion. Depression of external key 12 engages cap stem 13 and actuator nodules 32 through dome sheet 20 against switching membrane 22.
Referring more particularly to FIGS. 1B, 2B and 3, switching membrane 22 is comprised of a top layer 34, a spacer layer 36, and a bottom layer 38. A pair of opposed conductive switch contacts 40, 42 are provided on the underside of top layer 34 and top side of bottom layer 38, respectively. Contacts 40, 42 are positioned beneath dome 15 of dome sheet 20 and are depressible against one another through an opening 44 provided for such purpose in spacer middle layer 36.
A series of four isolated and conductive interdigiting electrodes 46 is formed on the underside of top layer 34. Each electrode region is positioned diagonally at the 45.degree., 135.degree., 225.degree. and 325.degree. positions relative to opposed contacts 40, 42, and collectively they form an outer shape of a square. Electrode regions 46 and actuator nodules 32 are positioned relative to one another such that respective nodules 32 engage in the respective centers of isolated electrode regions 46. A force-sensitive resistive polymer 48 is continuously provided about the top of middle layer 36 to correspond in positioning to electrode regions 46.
As evident from FIGS. 1A, 1B and 2A, 2B, depression of key 12 closes switch contacts 40 and 42, transfers pressing force against actuator 18, and correspondingly force to force-sensitive resistor regions 46 and 48 through actuator nodules 32. Actuator 18 is supported for limited angular tilting movement within mounting plate opening 19 for loading and unloading of various of the four conductive grid regions based upon where and how the operator depresses and angles key 12. The circuitry and software interprets the relative loadings of the various force-sensitive resistor electrode regions to impart cursor movement. Additionally, the quantity of force applied by the user affects conductivity through the respective force-sensitive resistor grid regions, with such information being used to impact the speed of cursor movement. The harder the depression applied by the operator, the faster the cursor movement.
The force versus resistance characteristics of the force-sensitive resistor of FIGS. 1-4 is illustrated graphically in FIG. 5. As evident, resistance drops as the amount of applied force increases. Also, force inputs at less than 200 grams fall on a significantly steep area of the curve. Accordingly, very minor changes in force in this area produce drastically different current flows, resulting in erratic or unpredictable operation. Equally important, a 200 gram pressure input by a user's finger is excessive and would not provide the desired and necessary tactile feel over the key for precise operator control of cursor movement. With the cursor movement control key FIGS. 1-4, such drawbacks or limitations are partially overcome by preloading the force-sensitive resistor to enable operator inputs significantly less than 200 grams and which enable more predictable operation for proportional operator force inputs.
Such preloading is achieved by or through the illustrated screws 24, screw plate 26, and tension spring 29 (FIGS. 1A and 1B). Screws 24 are slidably received through respective openings in screw plate 26 and thread into openings 27 on actuator 18. Spring 29 is sandwiched between screw plate 26 and the underside of backing plate 16. At manufacture and test, screws 24 are threaded sufficiently to draw actuator 18 against membrane 22 to provide a desired and equal preloading effect against each of electrode regions 46 such that reliable operation will be obtained with lighter operator force inputs. Such a construction is not however without drawbacks. For example, the requirement for adjustment increases problems and the time required at manufacture. Further, the construction could fall out of adjustment in operation, requiring the end user to attempt to readjust the required preload or effectively shorten the life of the key.
An additional drawback associated with the above-described construction relates to the diagonal positioning of electrode regions 46 relative to the orientation of the key. Such orientation in operation can provide less than desirable reliability when moving a key in the precise 0.degree., 90.degree., 180.degree. or 270.degree. positions, which are the predominant directions which operators move the cursor.
It would be desirable to overcome these and other drawbacks associated with cursor movement control keys for a computer having a video display which incorporate force-sensitive resistors.